Why in the world would you want to delete a tune when actually using the iPod? You'll never need extra space unless you're actually connected to a computer, in which case you can just launch iTunes and manually delete the songs you don't want via iTunes. Simple as that.
The point of the iPod is to be an MP3 PLAYER, not an MP3 ORGANIZER. There's a big difference, and the fact that the iPod doesn't put deletions and renaming and all that extra junk in the user interface makes it SO damn simple and easy to use. That's the whole point. It's part of the digital hub idea -- make two components, the computer and the iPod, easy to use, but when used in tandem, you can get so much more out of them. Otherwise you have a very confusing menu, and you could end up deleting a song that you didn't want to.
A VERY good implementation on Apple's port, IMHO.